Search for: low-earth-orbits
Article IET Radar, Sonar and Navigation ; Volume 10, Issue 7 , 2016 , Pages 1186-1190 ; 17518784 (ISSN) ; Kashani, E. S ; Ajorloo, A ; Sharif University of Technology
Institution of Engineering and Technology 2016
In triangulation (or angle of arrival) target localisation method, the surface of the Earth is approximated by a flat plate. This approximation, while acceptable for low-altitude observers (such as unmanned aerial vehicles), is not a correct model for high-altitude observers (such as low Earth orbit - LEO satellites). In this study, the authors have discussed triangulation method using a LEO satellite observer over a spherical surface and have shown that, using spherical trigonometry and singular value decomposition (SVD), a straight forward solution can be found for target localisation problem. Also, error bound is discussed and analysed using both SVD as well as simulation. © The...
Orbit Determination of LEO Satellites through Combining the SGP4 and HPOP Methods and Magnetic Sensor Data, M.Sc. Thesis Sharif University of Technology ; Salarieh, Hasan ; Alasti, Arya
Once the satellite is in space, it is very important to make sure that it is in its correct and prescribe orbit, along with the appropriate attitude, at any given point of time. Orbit determination and finding the exact position and velocity of a satellite is one of the most important factors in space missions. The purpose of this work is improvement in orbit determination of LEO satellites. In order to achieve this goal, combination of SGP4 and HPOP algorithms with Kalman filter is used. The HPOP algorithm uses from integration of equations of motion for finding the position and velocity of a satellite. So this algorithm is very accurate for the short time propagation, but since it is...
Controlling the attitude of linear time-varying model LEO satellite using only electromagnetic actuation, Article 2002 IEEE Aerospace Conference, Big Sky, MT, 9 March 2002 through 16 March 2002 ; Volume 5 , 2002 , Pages 2221-2230 ; 1095323X (ISSN); 078037231X (ISBN); 9780780372313 (ISBN) ; Momeni, H. R ; Sadati, N ; Baclou, H. G ; Sharif University of Technology
Recently small satellites are used more commonly because of the low launching cost and development of microelectronics. Also lower weight, size, cost and the power consumption of magnetorquer, has made the application of them in controlling attitude of the satellites common. Intensive changes and non-ability of geomagnetic field are some of the problems, which have limited the efficiency of magnetorquers. In this paper a new control method is presented that keeps the attitude of satellite in desired condition only by electromagnetic coils. The distinction of this method is its abilities in comparison with other methods. In this analytic method a direct relation between design parameters,...
M.Sc. Thesis Sharif University of Technology ; Asadian, Nima
In this thesis, the orbit determination of Low Earth Orbits (LEO) using the integrated magnetometer and horizon sensor data has been investigated. Orbit determination is an essential part of a space mission. Not only the modeling, guidance, navigation and control errors may results in error in injecting the satellite into its nominal orbit, the environmental disturbances deviate the satellite from its predicted orbit and from an operational perspective most satellites need continuous orbit determination. Traditionally, ground based orbit determination is used which are non-autonomous and expensive and just can be used for specific times which the satellite can be observed from the ground...
M.Sc. Thesis Sharif University of Technology ; Vosoghi, Bijan
Achieving technical knowledge and technology of design, build, test and launch satellites in each country is a strategic issue due to extension of satellite applications in various aspects of human life. One of the most important subsystems of a satellite is the telecommand part. This part is responsible for decode, receive, interpret, and distribution of commands and data received from the ground station. This part in terms of reliability is the most critical part of satellite because it coordinates satellite and ground station and also is the part which should be turned on during the mission and controls other parts of satellite. In other words this part should be design with high...
Article Acta Astronautica ; Volume 106 , January–February , 2015 , Pages 13-23 ; 00945765 (ISSN) ; Assadian, N ; Sharif University of Technology
Elsevier Ltd 2015
The estimation of the satellite orbital elements using the integrated magnetometer and horizon sensors data has been investigated in this study. These sensors are generally employed for attitude estimation. The magnetometer and the horizon sensor measure the Earths magnetic field as well as the Earths center direction in the body frame, respectively. The magnitude of the magnetic field and the angle between two vectors have been used for orbit estimation purpose. This excludes the knowledge of the attitude in the orbit determination. The Gaussian variation of parameters equations is used for the orbital motion dynamical model to have the orbital elements as the states of the system. Since...
Quaternion based linear time-varying model predictive attitude control for satellites with two reaction wheels, Article Aerospace Science and Technology ; Volume 98 , March , 2020 ; ISSN: 12709638 ; Nejat Pishkenari, H ; Salarieh, H ; Abdollahi, T ; Sharif University of Technology
Elsevier Masson SAS 2020
Attitude control of a satellite having only two reaction wheels is a challenging issue. To address this problem, previously published researches considered some simplifying assumptions on the satellites such as diagonality of the moment of the inertia matrix. On the other hand, in some works, the total angular momentum of the satellite is assumed to be zero. In this paper, a linear time-variant model predictive control (LTV MPC) is designed to control a satellite with two reaction wheels. This control method can be applied to a satellite with a non-diagonal inertial matrix in the presence of external torques, to rotate the satellite toward the desired directions in the space and orbit. The...
Article Advances in Space Research ; Volume 55, Issue 4 , 2015 , Pages 1028-1037 ; 02731177 (ISSN) ; Pourtakdoust, S. H ; Sharif University of Technology
Elsevier Ltd 2015
Accurate orbit determination (OD) is vital for every space mission. This paper proposes a novel heuristic filter based on adaptive sample-size Gaussian swarm optimization (AGSF). The proposed estimator considers the OD as a stochastic dynamic optimization problem that utilizes a swarm of particles in order to find the best estimation at every time step. One of the key contributions of this paper is the adaptation of the swarm size using a weighted variance approach. The proposed strategy is simulated for a low Earth orbit (LEO) OD problem utilizing geomagnetic field measurements at 700 km altitude. The performance of the proposed AGSF is verified using Monte Carlo simulation whose results...
Article Aircraft Engineering and Aerospace Technology ; Volume 81, Issue 2 , 2009 , Pages 137-148 ; 00022667 (ISSN) ; Mobed, M ; Sharif University of Technology
Purpose - The purpose of this paper is to propose a new guidance algorithm for launching a satellite using an expendable rocket from an equatorial site to an equatorial low-Earth orbit. Design/methodology/approach - Guidance during endoatmospheric portion is based on a nominal trajectory computed prior to take-off. A set of updating computations begins anew at the time instant tg of transition from endoatmosphere to exoatmosphere. The updating computations determine a guidance trajectory and an associated control law for the remainder of path by taking into account the rocket state at time tg. Thus, the overall guidance involves both initial and midcourse operations, and it has both open-...
Multidisciplinary design optimization of a satellite boom structure to reduce weight and vibration transmission using GA, Article 26th Congress of International Council of the Aeronautical Sciences 2008, ICAS 2008, Anchorage, AK, 14 September 2008 through 19 September 2008 ; Volume 3 , 2008 , Pages 2731-2741 ; 9781605607153 (ISBN) ; Abedian, A ; Sharif University of Technology
The weight of objects which are placed into low earth orbit should be closely managed historically a launch vehicles lift capability is fixed,so designers have paid close attention tothe weight of satellite subsystems to optimize the payload mass.Also due to applications of these structures,their performance against the vibrations is important.Simultaneous reductionof weight and band averaged vibration transmission in a satellite boom structure is the major task of the present study.This study approached the design problem by sizing periodic structureand geometric parameters to optimize the weight and system performance in a broadbandfrequency region using genetic algorithm (GA)
On-Line orbit and albedo estimation using a strong tracking algorithm via satellite surface temperature data, Article IEEE Transactions on Aerospace and Electronic Systems ; Volume 57, Issue 3 , June , 2021 , Pages 1443-1454 ; 00189251 (ISSN) ; Kiani, M ; Pourtakdoust, H ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc 2021
The Earth albedo factor (EAF) is a major required parameter for the thermal analysis of low Earth orbit satellites. Satellites receive variable albedo radiation as they orbit around the Earth that is heavily dependent on the Earth's local terrain as well as the instantaneous cloud coverage. However, for satellite thermal balancing and control analysis, a constant mean EAF is usually taken based on the orbital parameters that could potentially introduce erroneous results. Recent advances in temperature-based orbit estimation (TBOE) algorithms have revealed a significant sensitivity concerning EAF giving rise to the idea of its on-line estimation for added accuracy. In this sense, a novel...
Article Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering ; 2021 ; 09544100 (ISSN) ; Assadian, N ; Sharif University of Technology
SAGE Publications Ltd 2021
The attitude fault-tolerant control of a flexible satellite actuated by reaction wheels and magnetic torquer bars is investigated in this article. A low earth orbit is considered for moment perturbations such as drag and gravity gradient. Furthermore, the flexible panels attached to a rigid central body are modeled through the assumed mode approach by a finite set of bending modal motion. The ordinary differential equations of their generalized coordinates are found using Lagrange’s equation, and the resulting dynamical model is validated by comparing its simulation results to the NX Siemens software results. Finally, a fault-tolerant controller based on sliding mode control is suggested and...
M.Sc. Thesis Sharif University of Technology ; Alasti, Aria
Algorithms for online identification of parameters of a satellite’s moment of inertia tensor based on two methods (recursive least squares and Kalman Filter) is presented and compared with each other. It is assumed that the satellite actuators are three orthogonal reaction wheels. The only available sensor is a 3-axis rate gyro, which measures the angular velocity of satellite in body coordinate system. For validation of algorithms on earth, a similar identifier was designed for a satellite simulator. Due to difference in Dynamics of satellite and satellite simulator, capability of identifying center of gravity was added to algorithms. In order to account for friction in air bearing of...
Article Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering ; Vol. 228, issue. 13 , Oct , 2014 , p. 2385-2398 ; Assadian, N ; Sharif University of Technology
In this paper, an autonomous orbit control of a satellite in Low Earth Orbit is investigated using model predictive control. The absolute orbit control problem is transformed to a relative orbit control problem in which the desired states of the reference orbit are the orbital elements of a virtual satellite which is not affected by undesirable perturbations. The relative motion is modeled by Gauss's variational equations including J2 and drag perturbations which are the dominant perturbations in Low Earth Orbit. The advantage of using Gauss's variational equations over the Cartesian formulations is that not only the linearization errors are much smaller, but also each orbital element can be...
Article European Journal of Operational Research ; Volume 222, Issue 2 , 2012 , Pages 386-391 ; 03772217 (ISSN) ; Assadian, N ; Sharif University of Technology
In this study, the optimal burn time for low-thrust impulsive propulsion systems is investigated to raise the perigee altitude of a low-Earth orbit. The maneuver is done using spin-stabilized attitude control and impulsive thrusting system for a time interval centered about apogee point. On the one hand, the low value of the thrust level causes more burn time needed to accomplish the transfer. This, in turn, will cause more thrust loss due to the deviation between the thrust axis (spin axis) and the velocity vector of the satellite. On the other hand, for small thrust duration, the transfer needs more revolutions around the Earth and more travel in lower altitudes with dense atmosphere and...
Article Wireless Personal Communications ; Volume 62, Issue 4 , February , 2012 , Pages 793-804 ; 09296212 (ISSN) ; Rahimi, F ; Sharif University of Technology
Elevation angle is one of the most significant parameters of land mobile satellite channels, subject to rapid variations in the case of Low Earth Orbit (LEO) satellite systems. In this paper a novel trace-based framework is proposed and analyzed which is capable of predicting elevation angle as a function of time during satellite visibility window. Trace-time based modeling makes the framework practical for real-time evaluation of elevation angle and its alteration incurred by communication links in LEO satellite systems. The proposed method is particularly suitable for development of communication channel models and services in mobile LEO satellite networks where path variability is of...
Article Signal, Image and Video Processing ; Volume 11, Issue 3 , 2017 , Pages 565-572 ; 18631703 (ISSN) ; Bayat, S ; Farina, A ; Hajsadeghian, S ; Nayebi, M. M ; Sharif University of Technology
Springer London 2017
This paper presents a feasibility study on using satellite signal for passive radar application. Our focus is on utilizing geostationary Earth orbit satellite signal with suitable properties, like Inmarsat. Then, a new method of detection for passive coherent location using adaptive filter weights variation model is presented. To evaluate the performance, three different scenarios including a low Earth orbit satellite, a space shuttle, and a high-altitude aircraft as the targets of interest are considered. In addition to being covert, it will be shown that using such passive radar system, we can benefit the forward scatter enhancement, which enables us to detect such high-altitude targets...
On-line orbit and albedo estimation using a strong tracking algorithm via satellite surface temperature data, Article IEEE Transactions on Aerospace and Electronic Systems ; 9 December , 2020 ; Kiani, M ; Pourtakdoust, S. H ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc 2020
The Earth albedo factor (EAF) is a major required parameter for the thermal analysis of low Earth orbit (LEO) satellites. Satellites receive variable albedo radiation as they orbit around the Earth that is heavily dependent on the Earth's local terrain as well as the instantaneous cloud coverage. However, for satellite thermal balancing and control analysis, a constant mean EAF is usually taken based on the orbital parameters that could potentially introduce erroneous results. Recent advances in temperature-based orbit estimation (TBOE) algorithms have revealed a significant sensitivity concerning EAF giving rise to the idea of its on-line estimation for added accuracy. In this sense, a...